Vaccines against various and evolving strains of influenza are important not only from a community health stand point, but also commercially, since each year numerous individuals are infected with different strains and types of influenza virus. Infants, the elderly, those without adequate health care and immuno-compromised persons are at special risk of death from such infections. Compounding the problem of influenza infections is that novel influenza strains evolve readily, thereby necessitating the continuous production of new vaccines.
Numerous vaccines capable of producing a protective immune response specific for such different influenza viruses have been produced for over 50 years and include, e.g., whole virus vaccines, split virus vaccines, surface antigen vaccines and live attenuated virus vaccines. However, while appropriate formulations of any of these vaccine types is capable of producing a systemic immune response, live attenuated virus vaccines have the advantage of being also able to stimulate local mucosal immunity in the respiratory tract. A vaccine comprising a live attenuated virus that is also capable of being quickly and economically produced and that is capable of easy storage/transport is thus quite desirable.
To date, all commercially available influenza vaccines have been propagated in embryonated hen eggs. Although influenza virus grows well in hen eggs, the production of vaccine is dependent on the availability of such eggs. Because the supply of eggs must be organized, and strains for vaccine production selected months in advance of the next flu season, the flexibility of this approach can be limited, and often results in delays and shortages in production and distribution. Therefore, any methods to increase throughput and/or increase output of vaccine production in hen eggs is greatly desirable.
Systems for producing influenza viruses in cell culture have also been developed in recent years (See, e.g., Furminger. Vaccine Production, in Nicholson et al. (eds.) Textbook of Influenza pp. 324-332; Merten et al. (1996) Production of influenza virus in cell cultures for vaccine preparation, in Cohen & Shafferman (eds.) Novel Strategies in Design and Production of Vaccines pp. 141-151). While eliminating many of the difficulties related to vaccine production in hen eggs, not all pathogenic strains of influenza grow well in cell culture, or can be produced according to established tissue culture methods. In addition, many strains with desirable characteristics, e.g., attenuation, temperature sensitivity and cold adaptation, suitable for production of live attenuated vaccines, have not been successfully grown in tissue culture using established methods. Therefore, any methods to increase throughput and/or increase output of vaccine production in cell culture is also greatly desirable.
Considerable work in the production of influenza virus for production of vaccines has been done by the present inventors and co-workers; see, e.g., Multi-Plasmid System for the Production of Influenza Virus, U.S. Ser. No. 60/375,675 filed Apr. 26, 2002, PCT/US03/12728 filed Apr. 25, 2003 and U.S. Ser. No. 10/423,828 filed Apr. 25, 2003, etc. The present invention provides methods of increasing/optimizing production (in both quantity/quality and speed) of such viruses, as well as for other influenza viruses, for production of vaccine compositions. Aspects of the current invention are applicable to traditional hen egg and new cell culture vaccine production styles (and also combined systems) and comprise numerous other benefits that will become apparent upon review of the following.